WASHINGTON — Defense Secretary Caspar W. Weinberger, in an unusually sharp attack on fellow Republicans, Thursday accused GOP members of the Senate Budget Committee of making "a great political career or capital . . . of bashing the Pentagon."

Some Republicans on the committee, he declared, are unwilling to vote for spending cuts that affect their districts but then "hunt around" for excuses, such as defense contract scandals, to justify voting against the defense budget--just so they can still claim they are conservatives.

Cites Arms Talks

Weinberger, interviewed at a breakfast session at The Times' Washington Bureau, warned that slashing the Administration's proposed defense spending, as a budget resolution approved Wednesday by the Senate Budget Committee would do, would seriously undermine the efforts of U.S. negotiators at the current arms talks with the Soviet Union in Geneva.

When asked whether he thinks the Budget Committee is an "aberration" within the Senate, Weinberger quipped, "I like to think so," but he added that he takes the committee's opposition to his budget requests "seriously indeed."

"I think it's very unfortunate, very wrong and very serious," he said.

Republican critics of the defense budget have pointed out that, although the Reagan Administration has slashed domestic spending, it has increased defense spending dramatically--from $211 billion in fiscal 1982 to $292 billion in 1985. As do many Democrats, they contend that it would be unfair to make further domestic spending cuts without also reducing the Pentagon budget.

Moreover, they argue, defense spending could be reduced this year but, if necessary, increased next year.

'Let's Try It Again'

Weinberger, in rejecting that argument as "unrealistic," said: "If defense is hammered down this year below the levels that are really necessary, then I think you would have a lot of people saying, 'Nobody attacked us, so let's try it again.' "

Some Republicans who proclaim themselves conservatives, he said, "still feel it essential that they combine conservatism with support for defense, and yet they have a lot of desire to vote for higher agriculture subsidies, they worry about deficits--but they don't want to make any reductions of Amtrak, which serves their district, or other things that people are much more interested in directly."

Republicans on the Budget Committee, he said, will "hunt around for some excuse . . . that will enable them to proclaim very proudly that they're still conservatives and they want a strong defense, but they aren't willing to vote for a strong defense budget."

"So they'll find something very wrong, like a General Dynamics claim or a spare parts price that we never paid--that was published, however, as a price. They'll say, 'Look at this, this is dreadful, I'm not going to vote for a defense budget with that in it.' "

Never a Friendly Welcome

Weinberger, who noted that he could not recall "a genuine friendly reception" on Capitol Hill in more than four years of testifying on defense budgets, said that he does not know whether hostility in Congress to that budget has increased this year.

Despite senators making "violent statements at the hearings, a great deal of posturing, hurling themselves about" and saying defense must be included in the budget cutting, the Pentagon has managed to persuade Congress to approve about 95% of its budget requests during the last four years, he said.

Weinberger reacted jokingly at first when asked whether he had read charges of Pentagon waste made in an editorial page column in Thursday's editions of the Wall Street Journal by Sen. Charles E. Grassley (R-Iowa), a Budget Committee member who has campaigned for a freeze on the department's budget.

Rolling his eyes toward the ceiling, the secretary exclaimed: "No, what's he doing? Are there no journalistic standards left?"

But he heatedly dismissed charges by Grassley that the Defense Department's own records show that the some major defense contractors were paid for work done at only 5% or 7% of factory efficiency.

5,050 Hours for Job

Grassley wrote that the Pentagon "paid one major defense company working on the MX missile for 5,050 direct labor hours when its own factory efficiency data say the same work should take only 370 hours. That means we pay for 7% factory efficiency on work done by that contractor. This example is by no means unique."

Weinberger said that he was not familiar with those figures or others cited by Grassley, but he noted that the Pentagon has "very complete audits to make sure that overhead is not being inflated." He suggested that Grassley was talking about "one or two isolated incidents from the past."

It might be months before there is a final vote on the defense budget, Weinberger said, and, although he would not make a prediction on the outcome, he expressed hope that the Republican senators would change their minds about opposing his spending proposals.